盾构隧道双液同步注浆GPR检测模型试验

Model Test Study on GPR Detection for Cement-sodium Silicate Synchronous Grouting in Shield Tunnel

为探究超大直径盾构隧道双液(C-S)同步注浆的填充效果,控制地层损失并保证隧道结构具有良好的受力和防水性能,以江阴-靖江过江盾构隧道为工程背景,测试并分析了单/双液浆拌和后48 h内的相对介电常数和电导率的时变特征规律,结果表明:双液浆的电性参数比单液浆变化趋势更稳定,相对介电常数在注浆后12~48 h趋于稳定,测试时间内电导率值分布在4.12~5.47 mS·m^(-1)区间。搭建了含注浆体空洞和厚度凿薄2种缺陷的管片-注浆体-土体多层介质足尺试验模型,在模型高度方向0.8、1.0、1.2、1.4、1.6 m处分别设置5条测线,采用搭载400、900 MHz双频探地雷达(GPR)的车架随行式检测机构,对注浆后24、48 h注浆体开展探测试验;利用自主开发的TGIS软件对试验数据进行去除背景、滤波、增益等处理,结合基于有限时域差分法的gprMax数值模拟结果对比,从单道波形和成像结果两方面分析了不同频率和不同检测时间下GPR的成像规律及检测效果,发现注浆后48 h内的双液浆电性参数变化对GPR反射波形的相位和振幅影响较小,该时段内可作为双液浆检测的合适时机。注浆体厚度凿薄和内部空洞2种缺陷会造成GPR探测波形中同相轴中断和波动,通过GPR探测结果可对其进行良好辨识。与900 MHz相比,通过400 MHz的GPR探测对介质分界面和注浆缺陷的辨识效果更佳,900 MHz的波形对14 ns及更深环境的注浆体探测效果有限。

To investigate the effect of cement-sodium silicate(C-S)synchronous grouting,the time-varying electrical parameter characteristics of a single-liquid/C-S grout were tested and analyzed in the context of the Jiangyin-Jingjiang river-crossing shield tunnel.The results show that the electrical parameters of C-S grout have a more stable trend than that of single-liquid grout.The dielectric constant tends to stabilize within 12to 48h,while the conductivity values distributed range from 4.12to 5.47mS·m^(-1).A full-scale model test was conducted consisting of a multilayered medium of segments,grouting body,and soil layer,while two defects,grouting cavity and thin thickness,were also involved in the tests.Ground-penetrating radar(GPR)detection tests were conducted on the grouting body at 24hand 48hafter injecting along five different detection monitoring lines.Combined with a gprMax numerical simulation comparison,the imaging rule and detection effect of the GPR were analyzed under varying frequencies and detection durations.This indicates that the change in the electrical parameters of the C-S grout within 48hafter grouting has little impact on the phase and amplitude of the GPR reflection waveform,and the two defects of thin thickness and cavity cause interruption and fluctuation of the in-phase axis in the GPR reflection wave.GPR can be used for good identification,with better identification effect at 400MHz.However,the 900MHz waveform has a limited effect on grouting detection at 14ns and deeper.